Suppressing Dendritic Tic Growth in Cast Tic/Ti-7.8cr Matrix Composites Via Rare Earth Y Addition

Abstract

The fabrication of TiC-reinforced titanium composites via melting casting faces inherent challenges: constitutional supercooling promotes dendritic TiC growth, severely embrittling the material. This study introduces rare earth Y to react in-situ with oxygen, forming Y2O3, and investigates the microstructure-property relationships at different Y2O3 contents. The results showed that with the increase of Y2O3 content, its morphology gradually changed from granular to feather like. When Y2O3 (111)//β - Ti (110), the interface between the two had the lowest two-dimensional mismatch degree, with a value of 26.6%, belonging to a non coherent interface. During the solidification process, the dendrites of TiC mainly grow outward along the [100] direction. After adding Y to the composite material, Y2O3 formed aggregates at the tips of the primary and secondary dendrites of TiC, hindering the continued growth of its dendrites; In addition, some Y2O3 and TiC form a two-phase symbiotic structure, and Y2O3 and TiC compete with each other for growth, leading to difficulties in TiC growth. When the Y2O3 content is 0.5 wt.%, the composite material exhibits optimal mechanical properties, with Rockwell hardness and elongation at break of 39.4 HRC and 5.86%, respectively, an increase of approximately 5% and 17.9%, respectively.

Keywords: Titanium matrix composites, Microstructure, Y2O3, Mechanical properties